In SituRemediation of Sediments Contaminated with Organic Pollutants Using Ultrasound and Ozone Nanobubbles

Anin situremediation method was developed based on low-frequency ultrasound, and ozone nanobubbles to remediate heavily contaminated Passaic River sediments. This study evaluated the performance of the method to remediate organic pollutants in sediments. The ultrasound brings soil into suspension and causes desorption of contaminants from sediments due to both sono-physical and sono-chemical effects. Ozone oxidizes the desorbed contaminants to products that are water soluble and benign for removal by treatment and subsequent filtration. Nanobubbles are gas cavities in an aqueous solution with diameters smaller than 1 mu m. Ozone delivered as nanobubbles enhanced the mass transfer efficiency with long retention time in the aqueous phase when compared to use of commonly found bubbles. Simulated dredge sediments made of synthetic soil contaminated with a known concentration of p-terphenyl to represent polycyclic aromatic hydrocarbons was used to evaluate the proposed technology. Test results showed,with increased sonication power, and longer treatment time, increase in treatment efficiency. The addition of ozone nanobubbles significantly enhanced treatment efficiency when compared with only ultrasound. The prolonged sonication increased the solution temperature and decreased the dissolved ozone and nanobubble concentration. With higher power levels, in addition to the desorption of contaminants, there was breakage of soil particles. Hence, pulsed sonication was used, and ozone was added to the system in stages, before and after sonication. Test results showed a maximum treatment efficiency of 91.50% (initial p-terphenyl 1875 mg/kg) for 1.2 W/cm(3)ultrasound power over 4 h of sonication with 2-min pulses, confirmed the removal of organic pollutants in sediments.